The Aromatisation of Diacetylenes

Willis, Roland G (1962) The Aromatisation of Diacetylenes. PhD thesis, University of Glasgow.

Abstract

The thesis is divided into three parts. PART I. The base-catalysed isomerisation of hepta-1,6-diyne to toluene has been investigated using a variety of base-solvent systems. The best results were obtained by refluxing the diyne with a 10% solution of potassium t-butoxide in diglyme. A number of straight chain diacetylenes have been prepared and aromatised, by this method, to isomeric mixtures of mono- and o-disubstituted benzenoid hydrocarbons in which the most symmetrically substituted o-isomers predominated. The reaction is general for this type of diacetylene and the aromatic mixtures were obtained in 60-70% yield. The macrocycle, cyclotetradeca-1,8-diyne, and the dienyne, octadeca-9,12-dien-6-ynoic acid, also aromatise, but not the tetraene, ethyl arachidonate. A mechanism involving internal Diels-Alder cyclisation of a conjugated allene-diene intermediate is suggested. An empirical method of correlating the structures of isomeric o-dialkyl benzenes to their GLC retention times is put forward. PART II. 1,2,5,6-Tetrabromocyclooctane has been dehydrobrorminated with potassium t-butoxide in diglyme to a mixture of isomeric hydrocarbons containing mainly benzocyclobutene, styrene and a compound believed to be bicyclo[4.2.0]octa-1,3,6-triene. Cyclooctatetraene and an unknown compound are present in trace quantities only. This constitutes a new two stage synthesis of benzocyclobutene from readily available starting material. Cyclooctatetraene has also been isomerised under the same basic conditions to the same isomeric mixture as that above. An additional component, thought to be bicyclo[4.2.0.]octa-2,4,7-triene, is also present. The relative amounts of these components are dependent on the reaction temperature. This is the simplest synthesis of benzocyclobutene yet devised and the yield compares favourably with those obtained by other routes. PART III. The stereo mutation of cis to trans-undec-4-ene during hydrogenation over palladium catalyst has been investigated, and the extent of stereomutation related to the catalyst concentration. The hydrogenation of cis-undeca-1,7-diene has also been studied.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Organic chemistry
• Date of Award: 1962
• Depositing User: Enlighten Team
• Unique ID: glathesis:1962-79448
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Mar 2020 09:33
• Last Modified: 05 Mar 2020 09:33
• URI: https://theses.gla.ac.uk/id/eprint/79448